The human hip joint is capable of carrying loads exceeding several times body weight. The distribution of these loads over the load-bearing cartilage surfaces in the hip is of considerable interest in terms of studying the behavior of cartilage under various loading conditions and possible causes of osteoarthritis. A modified Moore prosthesis has been designed which is capable of measuring in vivo the spatial and temporal pressure variations generated by the loads carried by the hip. The pressures as meausred by this device will not only give a good indication of the pressure distributions that occur in the normal hip but will yield quantitative data on the pressures generated between the cartilage surface in the acetabulum and the ball of the prosthesis. The instrumented prosthesis consists of three main elements: a network of pressure transducers distributed over the surface of the ball, a multichannel telemetry device located inside the ball to transmit the information from the transducers to external receiving the recording equipment, and an electromagnetic power induction system which provides an external source of power for the telemetry device inside the prosthesis. In vitro versions of the prostheses are providing data, using both normal and diseased joints from human cadavers. Analytical models of the cartilage-bone-synovial fluid system are integrating and interpreting the experimental data.